FivePointOhh

ok with a .480 lift...what is stock spring lift? do i need a bigger spring on the gt40 head if the spring goes to .480? what size?

Scalihoo

RHS racing service's opinion , this article explains it allhttp://www.racingheadservice.com/Inf...adMaterial.asp

my77stang

actually your wrong, flow benches dont lie and the "thumper ported" E7's (which are total crap to begin with) will match or outflow the AFR 165's. if you start with a pair of 69-70 351w's or GT40's and have a quality port job they WILL flow better than the ported E7's - which means they will outflow the ARF 165's. That being said, obviously the AFR's can be ported for even larger gains, but now your into those heads for another grand or so.

I have early 351w's on what ws my 302 and will be my 289, with 1.84's/1.55's with serdi machined bowl work that was lightly blended by hand and the exhaust bumps removed. i can tell you that when those heads were on my 302 my little p.o.s. mustang II was light years faster than my 06 GT according to my *** dyno. since the 06's run high 13's outta the box, you can do the math.

OnyxCobra

I heard the ported GT40s were comperable to the AFR 165s, not the ported E7s. Yes AFRs cost more to start with but if you consider spending 300 on GT40 heads and another 600 or so maybe more for porting, i'd rather buy AFRs in the first place, and they are aluminum also and come factory CNC milled. Even though they flow comparibly to the AFRs I wasn't too impressed with the ET i saw from cars using the ported GT40s...

Blck92GT

Yes I realize thumper heads will outflow them, but unfortunately most people consider a port job letting a friend open everything up with a dremel with no consideration to air flow. Therefore they are getting no where near the performance gains they would with a CNC port such as powerheads or thumper.

my77stang

this is true, VERY true. this is exactly why my heads have porting limited to what is done to them. i can do machine work on heads like nobodies business, but i lack the hand porting skills i would want to possess to tackle my heads with a die grinder. i machine ported them myself, and then lightly went in the with hand tools to round any sharp radius left by the serdi. (and took out the exhaust bumps which isnt rocket science)

knowing when to leave something alone because you DONT know is a sign of true wisdom IMO. (i guess im smart, or something)

67mustang302

It's hard to compare different engines running different heads, you have to take into account the combination...comrpession ratio, piston type, combustion chamber type, quench height, cam profile, ignition, piston weight, rod weight, rod ratio, rotating assembly weight blah BLAH blah BLAH blah BLAAAAHHHH!!! There's a million different combos you could run, and which type of head/material works best depends on the combo. Aluminum will make the car a bit lighter(in the front end of already front heavy cars), will cool the combustion chamber faster, which means you can run higher CR or lower octane fuel realatively speaking. Iron retains more heat, which is better for a car that runs in colder climates mostly(Alaska etc) or is low compression. Aluminum(modern alloys anyway) are very strong and only warp if overheated repeatedly, otherwise the auto manufacturers wouldn't have switched to aluminum heads on so many cars today. As far as what to buy for performance, that would depend mostly on budget/performance goals. It's REALLY hard to beat out of the box aluminum heads these days using a factory type head. Especially since many of the head manufacturers have redesigned the head to not only change port volume, but port shape and combustion chamber shape as well. The biggest advantage most people see in aftermarket aluminum heads is you can buy it, slap it on and call it done and still make good power with little effort. It's not as simple as iron is better, or aluminum is better, it all really comes down to how the whole package is set up.

my77stang

wheres the fun in that? [8D]

67mustang302

Hahaha! True, I got my AFR 165's and the first thing I did was change out the springs on 'em. Anyway, I trust AFR's CNC machine more than any of the local machine shops

my77stang

its all in having quality work done. the only guy i would trust is my buddy who has his own shop and whos brother races in ARCA cup and used to race busch series. my buddy builds all the nascar style motors for those cars, and i have seen his port work firsthand on some old's heads and a ricer head. absolutely beautiful. problem is he's so overburdened with customer machine work getting him to devote time to a set of heads would cost a fortune